This invention relates to electrolyte and electrode materials for electrochemical current-generating cells, hereinafter referred to as electrochemical power cells.
Some electrical components, for example some electrode materials, are sensitive insofar as they are difficult to handle during manufacture of electrical devices owing to physical weakness or high chemical reactivity, which may necessitate inconvenient handling procedures and/or special conditions such as dry room assembly. Examples of such sensitive materials include alkali metals and alkaline earth metals, notably lithium metal electrodes for lithium cells. In one kind of such cells, the electrodes are assembled with sheets of polymer compositions which are inherently ionically conductive, often in liquid-free form commonly known as "polymeric electrolytes".
Lithium metal is difficult to roll into thin strips for use as an electrode, and U.S. Pat. No. 3,721,113 describes a method of alleviating this difficulty by rolling the lithium between smooth (surface asperities less than one micron) polymeric surfaces having sufficiently low critical surface tension to prevent adhesion to the lithium. The polymer may be a coating on the surface of rolls used to roll the lithium, or may be in the form of sheeting enclosing or facing the lithium, which does not adhere to the lithium and is peeled off the lithium strip after rolling. While this method facilitates the rolling operation, which produces the thin lithium strip, it does not improve the efficiency of assembling the delicate lithium strip into electrical devices.
Numerous variations of the materials and structure of individual cell electrodes have previously been described, with the emphasis on the chemical and electrical performance of the materials and with little attention to the assembly process itself. For example, British Patent No. 1533279 describes the use of an adherent thin coating of a vinyl polymer film on the surface of lithium strip electrodes for lithium/thionyl chloride cells to prevent electrode passivation, which tends to occur on storage of that particular kind of cell. The vinyl polymer film is insoluble in the thionyl chloride and must not be degraded or decomposed in the presence of the same. It must be sufficiently thin to permit ion transfer between the lithium and the thionyl chloride as required for current flow in operation of the cell. It is stated, though not demonstrated in the examples of the patent, that the vinyl polymer film may also serve as the sole electrode separator of the cell or may permit the use of a thinner separator than would normally be required. Somewhat thicker films of the vinyl polymer are recommended for that purpose, but it is made clear that the ion transfer needed for acceptable electrical performance of the cell will be adversely affected by thus increasing the film thickness. Electrode separators of polystyrene are described in U.S. Pat. No. 4,315,602 for alkaline cells, the separators again being necessarily thin enough to permit ion transfer.
French Patent No. 7832978 (Publication No. 2442513) describes preparation of polymeric electrolyte films and their application to reactive metal electrodes by techniques such as solvent casting or pressure lamination of the polymeric film onto the metal or flowing the molten metal onto the polymer film and cooling.